In the quest for hard surface cleaners which have efficacy against a variety of soils and stains, various heavy duty liquid cleansers have been developed. As an example, U.S. Pat. Nos. 3,985,668, 4,005,027 and 4,051,056 all issued to Hartman, show a combination of perlite (an expanded silica abrasive, which is here used as a filler), a colloid-forming clay, in combination with a hypochlorite bleach, a surfactant and a buffer in which abrasives are suspended. A clay thickened system of this type tends to set up or harden upon storage due to the false body nature of the thickeners, and requires shaking before use to break down the false body structure. Other prior art cleaners which attempt to suspend abrasives use either inorganic colloid thickeners only, or high levels of mixed surfactant thickeners. Syneresis often becomes a problem as the solids portion of such cleansers substantially separate from the liquids portion. One way to alleviate this is to use a perlite type material with specified particle size as defined in Hartman, 668. Additionally, high levels of surfactants can be used to form a plastic rheology for suspension of abrasives. However, they also have a detrimental effect on hypochlorite stability. For the instant purpose, half-life stability is defined as the amount of time it takes for 50% of the initial amount of bleach present in a given composition to decompose.
U.S. Pat. No. 4,287,079, issued to Robinson, relates to a clay/silicon dioxide thickened, bleach-containing abrasive cleanser which could contain an anionic surfactant. Due to the clay-thickened rheology, cleansers of this sort quickly dry out and set up. While these type of cleansers thus become less flowable over time, they are unfortunately also plagued by significant syneresis problems. U.S. Pat. No. 3,956,158 to Donaldson shows an abrasive-containing bleach thickened with insoluble detergent filaments. Chapman, U.S. Pat. No. 4,240,919 describes a liquid abrasive scouring cleanser with a thixotropic rheology and discloses a multivalent stearate soap to provide the thixotropic rheology. Such stearate thickened systems exhibit poor phase stability at temperatures above about 90.degree. F. The formulation of Chapman includes an aluminum oxide abrasive of a 400 micron particle size, which is not colloidal therefore cannot be used to suspend abrasive. Gel-like liquid automatic dishwasher detergents are disclosed in Baxter, U.S. Pat. No. 4,950,416; Drapier et al., U.S Pat. No. 4,732,409; and EP 345,611 to Delvaux et al. (published Dec, 13, 1989). Drapier et al. and Delvaux et al. disclose aluminum, magnesium, or zinc stearates to improve phase stability of liquid, gel-like, clay thickened dishwashing detergent, and to improve cup retention properties, i.e., to increase yield stress. The compositions of Drapier et al. and Delvaux et al. are clay thickened, phosphate-built thixotropic detergents, which differ significantly from the colloidal alumina thickened, plastic rheology of the compositions of the present invention. The phosphate builder system disclosed by these references is incompatible with a calcium carbonate abrasive. Baxter also discloses C.sub.8-22 fatty acids or their aluminum, zinc or magnesium salts to increase yield stress and cup retention properties of an automatic dishwashing detergent which is thickened with a colloidal alumina. Like Drapier et al. and Delvaux et al., however, the compositions of Baxter are phosphate based, and do not include an abrasive. While employing colloidal alumina as a thickener, Baxter uses only small amounts of surfactants for their cleaning funtionality, thus results in a thixotropic rheology, as compared with the plastic rheology of the formulations herein.
The disclosures of U.S. Pat. Nos. 4,599,186, 4,657,692 and 4,695,394, all to Choy et al., teach the use of an inorganic colloid combined with a surfactant/electrolyte system to provide good physical stability. These patents are commonly owned herewith and are incorporated herein by reference.
In view of the art, there remains a need for improving long term viscosity stability in liquid abrasive cleansers having colloidal alumina thickeners.